best in category (opinion):
Raider - Glaive: cost effective, versatile, fast, a prime staple of what a raider should be.
Skirmisher - buoy: A skirmisher that slows on hit and is tanky? oh man.
Riot - Reaver: it's a walking stardust!
Artillery - Badger: being able to stockpile your payload into a spot and have it spring at a moments notice with cloaked tech is ridiculous
Assault - Minotaur: EXTREMLY tanky in armor and packing a huge punch, it has the grit necessary to break a line in two.
Specialty - Dominatrix: nothing is more rude than seeing that unit you spent so long in making only for it to be converted
Super-unit - Paladin: having several ways to crowd control and can fight most units easily, it makes for quite the threatening presence
Aerial - Lhiko: nothing says "go away" like a tact nuke straight for your foes.
Sea - Duck: Quack quack you got an anti-sub and a raider all in one package.
Worst in category (opinion):
Raider - Pyro: expensive and unless heavily micro managed, this raider's quite a difficult thing
Skirmisher - Rouge: while powerful in payload, it is VERY slow in velocity and has to arc its shots.
Riot - Outlaw: delivering quite the slowing field and repeatedly doing so, it's not too hard to overwhelm this riot.
Artillery - Firewalker: what it lacks in direct hits it makes up in burn damage, which, can be spread way too thin at times.
Assault - Ravager: while speed the name, dying fast is also this thing's game.
Specialty - Limpet: the most things can be slowed by is 50% and how easily detected this is, it's quite difficult to use this efficiently.
Super-unit - Detriment: by the time you sunk in the metal to make this thing the enemy is mass producing raiders to bite at your ankles and distract you greatly.
Aerial - Phoenix: only good at telling raiders or workers to go away, but that's about it.
Sea - Seawolf: very effective up until the enemy starts making ducks or scallops, then that's where this thing plummet into the depths, also it has navigational problems if the water's too shallow.